1. Technical Field
The present invention relates to illumination fixtures and particularly to an illumination fixture using light emitting diodes (LEDs)
2. Description of Related Art
High intensity discharge (HID) lamps are widely used for illumination in public areas because of the high efficiency available, e.g. 100-140 lumens/watt. HID lamps are supplied from mains voltage by HID ballast circuits installed in or in the vicinity of HID lamp fixture. Modern HID ballasts are microprocessor controlled, i.e. circuit blocks include transistor switches, e.g. gates of MOSFETS, which are controlled by a microprocessor.
FIG. 2 is a cross-sectional view of a conventional HID lamp fixture 200 employing a high intensity discharge lamp (not shown) mounted at the base of a reflector 4a with a lamp holder 38. Lamp holder 38 connects to power terminal 20a on wires between terminals 38a and 38b and terminal 20a. Power terminal 20a provides the connections to ballast circuit 20b. Cable glands in cable gland apertures 18 allow cable entry of electrical cables into housing 2 for termination of cable cores inside housing 2 in terminal 20a for example. Cable glands in cable gland apertures 18 also allow cables or cords to be firmly secured to housing 2. Reflector 4a is constructed to reflect downward the light emitted from the HID lamp. Ballast circuit board 20b which supplies an ignition voltage used to ignite the lamp, typically a high voltage and an operating current which operates the lamp subsequent to ignition. HID lighting fixtures are typically attached using eye 16 approximately 5-7 meters above the surface of the floor to provide indoor lighting.
Although an efficient light source, the use of HID lamp technology has several disadvantages. HID lamps require several minutes to warm up. When the HID lamp is initially cool, an ignition voltage of 3000-5000 volts for instance is typically required to ignite the HID lamp. A re-ignition for the same lamp when the lamp is still hot, may require up to 20,000 volts for re-ignition to occur. The re-ignition when the lamp is still hot may also require a different frequency or phase characteristic for the ignition voltage to avoid risk of blowing up the HID lamp. Lamps and ballasts with hot re-strike capability are much more expensive then ballasts and lamps without hot re-strike capability. Under a drop of mains voltage, when hot re-strike is not used or unavailable, HID lamps remain off for five to ten minutes while they cool down before re-ignition. While HID lamps are in the process of cooling down, other lighting is used which supplies sufficient light just after the mains voltage comes back on. Quartz-halogen lamps are often used for emergency lighting which are lit while the HID lamps are cooling down and waiting for re-ignition. The quartz-halogen lamps require different wiring and fixtures from the HID lamps.
Further, some HID lamps, such as mercury halide lamps may pose an environmental hazard, in that the bulb materials include mercury. This mercury has to be safely disposed of when the metal halide bulb is no longer usable in fixture 100.
Thus, there is an advantage and a need to replace HID lighting with LED lighting.
LEDs are becoming more widely used in consumer lighting applications. In consumer applications, one or more LED dies (or chips) are mounted within a LED package or on a LED module, which may make up part of a low power LED lighting fixture, typically less than 50 Watts which includes one or more power supplies to power the LEDs. Various implementations of LED lighting fixtures are becoming available in the marketplace to fill a wide range of applications. LEDs offer improved light efficiency, a longer lifetime, lower energy consumption and reduced maintenance costs, as compared to HID light sources.